Biology Of Glomus Tumors Pathology

Macroscopically, glomus jugular tumors are typically tan-gray to purple, encapsulated, vascular, and lobulated masses. Native glomus tissue and glomus tumors are derived from the embry-ological neural crest cells. Like the normal glomus tissue, glomus tumors are histologically indistinguishable from carotid body tumors and often display the histologic pattern referred to as Zellballen, with clusters of chief and sustentacular cells.5 Nuclear pleomorphism, hyperchromatism, and mitoses may not imply aggressive behavior. Rather, malignancy is defined as the presence of metastasis to an organ without paraganglia (versus multifocal) and occurs in fewer than 10% of cases.40 The distinction between multifocality and metastasis is illustrated by the example of a patient with a second glomus tumor in the lungs. The pulmonary lesion may not represent metastasis, as native glomus tissue is purported to occur in many locations, including the peribronchial tissue. Because of their slow growth, glomus tumors are somewhat insensitive to radiotherapy, but radiation does afford some degree of tumor control.

Anatomic Origin and Distribution of Glomus Tumors

Rockley and Hawke41 carefully studied the anatomic distribution of glomus bodies, and concluded that the division of glomus tumors into tympanicum or jugulare types is an arbitrary clinical classification, not reflecting the true anatomic distribution of glomus bodies. These workers proposed that "glomus bodies" are localized along the adventitia of the jugular dome, the tympanic branch of the glossopharyngeal nerve (Jacobson's nerve), and the auricular branch of the vagus nerve (Arnold's nerve).42 Tumors arising along Jacobson's nerve or the promontory of the middle ear are of the glomus tympanicum type, whereas those arising proximal to Jacobson's nerve in the inferior tympanic canaliculus (adjacent to the jugular bulb) are of the glomus jugulare variety. Glomus bodies located along the course of Arnold's nerve adjacent to the facial nerve account for the occasional tumor in the descending facial canal.43 Rarely, tumor can arise from glomus tissue in the vagus nerve (i.e., glomus vagale).44 The ascending pharyngeal artery, through its inferior tympanic branch, is the primary blood supply to glomus tumors.30'31 Additional blood supply is derived from the postauricular, occipital, internal maxillary, vertebral, and internal carotid arteries.45

Glomus jugulare tumors usually arise in the region of the dome of the jugular bulb, gradually filling this region and then expanding into the lateral compartment of the jugular foramen.

The fibro-osseus partition in the jugular foramen is generally intact in patients with small and medium-size lesions, thereby leaving the nerves well protected medial to the tumor. This represents a surgically less demanding location, as it is possible to dissect the tumor from this partition without exposing the lower cranial nerves.14 Large glomus jugulare tumors invade the anterolateral compartment of the jugular foramen and either render the lower cranial nerves dysfunctional or place them in jeopardy during tumor removal. Tumor can transgress the epineurium or even invade the actual nerve substance.14,46

Glomus jugulare tumors are locally invasive. After invasion of the temporal bone and middle ear, tumor can extend via the following routes: (1) down through the eustachian tube into the nasopharynx and skull base foramina; (2) along the ICA into the middle cranial fossa; (3) through the tegmen tympani to the middle fossa floor; (4) along the internal jugular vein or the hypoglossal canal into the posterior fossa; and (5) through the round window of the labyrinth with extension via the internal auditory canal into the cerebellopontine angle.45,47

Glomus Tumor Hormonal Activity

Glomus tumors may be endocrinologically active. Serum testing shows that approximately 4% of patients with these tumors have elevated catecholamine concentrations.48 Because of this endocrinologic activity, glomus tumors have been included in the amine and amine-precursor uptake decarboxylase series (APUD) or, by newer terminology, the diffuse neuroendocrine system (DNES).42,49,50 Immunohistochemistry stains may demonstrate positive numerous markers including neuron-specific enolase (NSE), serotonin, chromogranin, leu-enkephalin, gastrin, substance P, vasoactive intestinal peptide (VIP), somatostatin, bombesin, melanocyte-stimulating hormone (MSH), and calcitonin.50

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